My goal is to incorporate as many relevant demonstrations into the classroom as possible. Here are photographs of some demonstrations that I have done. Caution: The descriptions of these potentially dangerous demonstrations are incomplete. If you have questions about these demonstrations or suggestions please contact me at campbell@bradley.edu.

Vitamin C Cleans Up Iodine Stains on Hand

I learned this demo from a visitor to campus a couple years ago. This demo takes only a couple minutes. To put this together, you need to go to the local drugstore/grocery store and pick up the following:

-iodine solution (tincture of iodine, used as a disinfectant)

-spray starch

-vitamin C tablets

Step 1 - Smear some of the iodine solution on the palm of your hand. DO NOT let the iodine solution dry out (otherwise it will be hard to remove).

Step 2 - While the iodine solution is still wet, spray some starch onto the palm of your hand. The iodine spot turns blue-black as the starch molecules wrap around the iodine molecules. Again, DO NOT let this mess on your hand dry out.

Step 3 - While the iodine/starch solution is still wet, take a vitamin C tablet and rub it across the stain (I make a smiley face first). The dark stain disappears though sometimes there might still be some yellow tint left. The vitamin C tablet acts as an antioxidant, reducing the iodine to iodide ions and breaking apart the starch/iodine complex. The tablet itself stays fairly white, this it not simply rubbing the stain off, it is a chemical reaction.

CAUTIONS:

Wash your hands with soap and water as soon as you get the chance after the demo (the starch on your hand will still be sticky/slimy).

Iodine stains all sorts of things, so do not spill it.

DO NOT eat the vitamin C tablet that you used in the demo, though you should be able to use the same tablet multiple times.

You should try this demo by yourself first in case I missed any subtle details.

VARIATION: A counterfeit money marking pen, which apparently contains iodine, can be used instead of tincture of iodine. The iodine in the pen does not react with the cloth fibers in real money, but it does react with the cellulose fibers in counterfeit money. The pen can be used to draw light tinted patterns on skin, but the markings dry out fairly quickly so the starch must be applied quickly to turn them dark. These starch/iodine marks can also be erased with a vitamin C tablet.

ABOVE: (LEFT) Step 1 (MIDDLE) Step 3 and (RIGHT) Variation: Erasing counterfeit money pen marks.

 

Coin Batteries

These batteries are simply voltaic piles made by stacking alternating types of coins with filter paper soaked in saturated salt water solution. The metal compositions of pennies are sufficiently different from nickels so that these coins may be used to make weak batteries. More coins can produce more voltage, but there is a tremendous variability in the actual voltage measured. This is likely due to effects such as internal resistance and degree of corrosion on the coins.

See: Scharlin, P.; Battino, R.; Boschman, E. J. Chem. Educ. 1991, 68, 665.

 

ABOVE: (LEFT) A simple coin battery - a nickel on salt-water soaked filter paper on a penny. (MIDDLE) Measuring the potential of a single pair of coins (in millivolts). (RIGHT) Measuring the potential of multiple pairs of coins (in millivolts).

Iron Filings in a Sealed Bottle

A couple of years ago I placed coarse iron powder in a sealed bottle to use in magnetism demonstrations. Recently I noticed that the bottle had partially collapsed and hypothesized that it the oxygen in the bottle's air had oxidized the iron to produce iron oxide. I used the volume displacement method (a large graduated cylinder partially filled with water) to estimate the gas volume in the collapsed bottle (405 mL) and in the bottle after allowing air to refill the bottle (490 mL). This represents a percent gas volume change of 17%, which is in the ballpark of the typical 21% oxygen concentration for air.

 

ABOVE: (LEFT) Partially collapsed bottle containing iron powder. (RIGHT) Reinflated bottle containing iron powder.

 

Demonstration Pictures: Page 1, Page 2, Page 3, Page 4, Page 5, Page 6, Page 7

 

Link to pictures of LEGO demonstrations

Return to Dr. Campbell's Favorite Demonstrations

Last updated 9/19/07

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